Many processes have been developed for producing hydrocarbons from various hydrocarbonaceous materials such as oil shale and tar sands. Historically, the dominant research and commercial processes include above-ground retorts and in-situ processes. More recently, encapsulated impoundments have been developed for recovering oil from crushed oil shale (In-Capsule® technology). These impoundments are formed primarily of earthen materials, with the crushed oil shale being encapsulated by an impermeable barrier made of rock, soil, clay, and geosynthetics, among other materials. The encapsulated impoundments can be very large, sometimes occupying several acres.
Generally, methods for recovering hydrocarbon products from oil shale have involved applying heat to the oil shale. Heating oil shale allows kerogen in the oil shale to break down through the process of pyrolysis, yielding liquid and vapor hydrocarbon compounds. Heating is also used to recover hydrocarbons from other types of hydrocarbonaceous materials, such as tar sands, coal, lignite, bitumen, peat, and other organic rich rock. Various heating methods have been used. For example, in-situ combustion of hydrocarbons, steam injection, hot combustion gas injection, closed-loop heating conduits, radio frequency heaters, electric heaters, and other heating systems have been used. Encapsulated impoundments in particular have included closed-loop heating conduits. An impoundment can include a body of crushed oil shale or other hydrocarbonaceous material with heating conduits buried in the crushed material. The heating conduits can be connected to a source of heat exchange fluid, such as hot combustion gases. The heat exchange fluid can flow through the conduits, transferring heat through the conduits to the body of crushed material. Heating the hydrocarbonaceous material in this way can produce hydrocarbon liquids and vapors, which can then be recovered from the impoundment.